U.S. Pat. No. 4,542,291 entitled "Optical flex sensor" discloses a sensor which consists of a flexible tube that has open ends and a reflective interior wall within the flexible tube, a light source placed within one end of the flexible tube and a photosensitive detector, or light transmitting device such as an optical fiber is placed within the other end of the flexible tube so that the intensity of a combination of direct light rays and reflected rays may be detected when the flexible tube is bent. The nature of the photosensitive detector is to change its resistance with light intensity. The combined effect of the bent tube on the light path and the photosensitivity of the detector produces a device that changes its electrical resistance when flexed.
U.S. Pat. No. 4,414,537, entitled "Digital data entry glove interface device", discloses a man-machine interface and in particular an interface that permits a user to input data, including alphanumeric and control information, with increased ease and efficiency to electric typewriters, computers, terminals and other types of data utilization devices. The disclosure describes a man-machine interface for translating discrete hand positions representing data characters into corresponding electrical signals. A knuckle-bend sensor is described as a part of the device which reacts to the stress produced on the data entry glove by flexing the corresponding joint. The disclosure states that such a device might use optical, Hall effect, conductive elastomeric, or strain gage sensors.